Counterbalancing mechanism for lift bridges



De 28, 1937, T. E. BROWN, JR

COUNTERBALANCING MECHANISM FOR LIFT BRIDGES Filed March 14, 1954 3Sheets-Sheet 2 INVENTOR mama; 55/0 ATTQRNEY T. E. BROWN. JR

GOUNTERBALANCING MECHANISM FOR LIFT BRIDGES Dec. 28, 1937.

Filed March 14, 1934 3 Sheets-Sheet 3 'INVENTOR z hwaff 5 6M ATTORNEYPatented Dec. 28, 1937 UNITED STATES GOUNTERBALANCING MECHANISM FOR LIFTBRIDGES Thomas E. Brown, J12,- Tuxedo, N.'Y. Application March 14, 1934,Serial No. 715,458

6 Claims. (01. 14-42) The invention relates to lift bridges and likestructures having a part which is caused to rise and fall by means ofpower applied thereto, and it relatesmore especially to thecounterbalancing means employed in connection therewith.

Various expedients have been proposed for counterbalancing the varyingload imposed by the V usual counterweight as utilized incounterbalancing the weight of the span of such structures and whichresults from weights of the changing lengths of wire ropes, chains orother flexible connections between said usual counterweight and thespan. These expedients, which comprise counterbalancing chains,auxiliary ropes with auxiliarycounterweights, etc., are all open to oneor more of many objections, such as high cost, inexactness of balance,imposition of horizontal loads on the towers and piers, etc.

The present invention has'for an object the provision of a simpleandeffective means for maintaining a substantially exact balance of theentire lift structure in all of its various positions and which means ispositive in its action.

.A further object of the invention resides in the provision of balancingmeans which may be economically installed and whereby imposition ofhorizontal load components is obviated.

In carrying out the invention, provision is made for a counterweightauxiliary to the main counterweight which acts directly upon thevertical lift span, said main counterweight introducing, as is usual,varying loads on the span in different locations of the latter relativeto its associated pair of towers. This auxiliary counterweight isarranged to be connected with the span through a drum rotatably mountedupon a tower and provided with a spiral groove portion, there beingprovided to this end also a plurality of flexible connections as ropesof wire or fibre connected with said drum, the. auxiliary counterweightand span. Or, sprockets and chains may be utilized instead.

One of said ropes adapted to run in the spiral groove portion of thesaid drum whereby the moment resulting from a load on this. rope willvary in accordance with the length thereof coiled in said groove, whichmoment thus may be designed to be proportionate to the unbalancing due Ito said main counterweight. The nature of the invention, however, willbest be understood when described in connection with the accompanyingdrawings, in which:

Fig. 1 is a side elevation of a vertical lift bridge equipped with thenovel balancing mechanism.

Fig. 2 is an enlarged part side elevation and part vertical section of adrum element constitut ing a member of the'novel mechanism; and Fig.

3 is an end elevation thereof. i

Fig. 4 is a side elevation of a vertical lift bridge illustrating amodification in the application of a the novel balancing mechanism.

Fig. 5 is an enlarged part side elevation and part vertical section of amodified form of a drum element and sheave utilized therein; and. Fig. 6is an end elevation thereoff I 10 Figs. 7, 8 and 9 are fragmentary sideelevations illustrating modifications. V

Referring to the drawings, more particularly Figs. 1 to 3 thereof, Illand II designate a pair of towersbetween which is mounted to movevertically a span i2, the latter being indicated in full line in itslowermost position and in dotted lines in the raised position. The spanis suitably counterweighted, as hereinafter set forth, to movevertically between these towers; and various ar- 20 rangementsof motorand connections may be utilized for effecting the lifting and loweringof the span, these mechanisms being omitted from the drawings for sakeof clarity and as they are well known and form no particular part of the25 present invention.

One or more main counterweights l3 maybe provided for counterweightingthe load set up by span l2, as through ropes I l attached, for example,at opposite ends 15 thereof. These ropes 30 are brought in the usualmanner over sheaves l6 rotatably mounted in the corresponding towers,preferably a pair at each end of the bridge; and the free ends of theropes are attached to the respective main co'unterweights. 5

In the particular embodiment illustrated in 3 Figs. 1 to 3, and inaccordance with the invention, a tower carries an auxiliary rotatabledrum 20. This auxiliary drum supports through a rope 2| attachedthereto, as at 22, an auxiliary counterweight 23; and a second rope 24attached to the drum at 25 is arranged to be connected with the span, inthe present embodiment at the point 26 substantially where the ropes Mare attached. The'said auxiliary drum, which is mounted 'to 45 rotateupon an axle 21, or by means of trunnions, and supported by a tower, isprovided with a spiral cone groove portion 28 and a helical grooveportion 29 of constant radius and in which, grooves the respective ropessecured to the drum 50 are adapted to run. For example, in the presentembodiment, rope 2! runs in the cone spiral groove portion and the rope24 in the helical groove portion. 7 Suitable guides 39 and 3'! may beprovided along the corresponding towersfor accommodating the respectivecounterweights i3 and 23 in their reciprocations.

In the operation of the mechanism hereinbefore described, it will beappreciated that, as span l2 rises, the descent of the counterweights l3and 23 will cause rotation respectively of the sheave l6 and drum 26,This, in the case of the drum, will cause rope 2i not only to unwindfrom the drum but in so doing will cause its contacting portion to bearin the groove of the drum at a different radius or distance from theaxle 27 due to the spiral character of this groove. The moment appliedby the auxiliary counterweight 23 through this radius upon the drum as'awhole will therefore vary accordingly, and a difierent lifting effortwill be applied from the auxiliary counterweight to the span-decreasingas the span rises, and being at a minimum when the span is in itsuppermost position, as indicated by the dotted line position, Fig. 1 ofthe drawings.

This effectively counteracts the increasing load developed by the maincounterweight it, due to the increasing length of rope Hi on thecounterweight side of the sheave, the curve of the groove 28 being soproportioned with respect to the weight of counterweight 53, its ropes Mand counterweight 23 as to cause the change in the upward force duringany motion of the span to equal the unbalance caused by the movement ofthe rope it over. the sheave it.

The upward stresses at points 26 are also affected by the weights ofropes 2i and 2 3 as they wind and unwind from drum 28. If the weights ofthese ropes be sumcient to materially afiect the required power tooperate the span, compensation for their effect may be had bymodification of the curve of groove 28.

To determine the required lever arms through which the ropes 2i act forthe various positions of the span, I first choose such proportions forthe extreme positions as will satisfy the conditions of balance in thesetwo positions, i. e., if'

m and H equal respectively the weights per unit of length of ropes 2iand 26, H the height of rise of span l2, and H and H equal respectivelythe total lengths of the ropes 24 and 2! that are respectively wound upon and unwound from drums it during the complete motion of the span,then H=H; and the proportions must meet the conditions of balanceexpressed by the for-' mula (2p+n)H=% (W1Wl-mHl) 2pH= (1 1")(nH+ f whereW represents the weight of the auxiliary counterweight 23; p the weightper unit length of ropes M; r the radius of the groove 29 about the axisof rotation of the drum and i, i l" the various lever arms, about saidaxis, of the center line of rope H as it unwinds from the conical groove28l being the lever arm corresponding to the lowered position of thespan, l the lever arm corresponding to the fully raised position of thespan, and i the lever arm corresponding to an intermediate position.

It will readily be seen that the stress in rope 2 caused by the saidweight 23 acting through rope 2i and drum 2% is W times its lever armdivided by r. This stress is communicated to the span by rope 2 3 andproduces an upward force on the span at point of attachment 2%. As thespan rises and rope 2i unwinds from groove aioaeei 28, the lever arm ichanges causing a change in this upward force. The curve of groove 28 isto be so proportioned with respect to the weight of counterweight 23 asto cause the change in this upward force during any motion of the span,to equal the unbalance caused by the movement of the ropes i in passingover the sheaves iii.

The proportions having been chosen to meet the aforesaid requirementsfor the extreme positions of the span, the curve of groove 28 isdetermined by finding the required lever arms for various intermediatepositions, as follows:

If h be any rise of the span 62 from its closed position, and h be theamount of rope 2i unwound from drum by such rise, then the requiredlever arm l to maintain the balance is If the weights of the auxiliaryropes 2| and 2% be so inconsiderable that they may be neglected, thenthe proportions to satisfy the extreme conditions become W 2pH= -(1-1),

and the lever arm for any intermediate position Many variouscombinations and mechanical arrangements can be made with my device.

In Figs. i to 6, a modification is illustrated in connection with thearrangement of the ropes and the auxiliary drum. The main counterweight33 is connected over the sheave to the span as in the previouslydescribed embodiment; and it is guided in its travel by the guide member33. Thus, the cone spiral-groove portion having the grooves 35 is inthis instance adapted to receive the rope 35 which is attached to thespan as at 3?, while the helical groove portion having the grooves 38 ofequal radius receives the rope 39 attached to the auxiliarycounterweight. The auxiliary counterweight ii! will therefore movevertically in straight lines, being guided by the guide member it; andbecause of the varying radius of the grooves 35, the ropes 36 will havea varying angle to the vertical in accordance with the position of thespan. Depending upon the proportions chosen, a rope 36 may be made toreach or to pass through the vertical position, indicated by the dottedline position, Fig. 5; but it is preferred to so choose the dimensionsthat a said rope will be vertical or nearly so when the span is in itsextreme elevated position.

This angle of deviation from the vertical will, of course, affect thevertical component of the pull of a rope on the span, which effect maybe readily computed and compensated for, but in the majority of casesthe effect thereof will be inconsiderable.

It will be understood, furthermore, that for any given set of conditionsthe smallest radius of both grooves of an auxiliary drum may beincreased by constructing both of the sets of grooves of the drum of aspiral character, thereby permitting the use of a larger size of ropes.

In Figs. 4 to 6, a sheave 3 1 for the main counterweight and a drum forthe auxiliary counterweights have been indicated as rotatable about thesame axis; while in Fig. 7 they are arranged one behind the otherwhereby the rope t! from the auxiliarydrum 62 may be attached to themain counterweight 43 which in turn is attached by rope st to the span45. Theeffect of the auxiliary counterweight =36 is thereby transmittedto the main counterweight 43 by means of the ropes 4i and 47, instead ofdirectly to the span es. With this arrangement, the effects of the twocounterweights are opposed and the auxiliary counterweight effects anincreasing lift on the main counterweight as the latter falls with therise of the span. Also, but a single connection is required to the spanfrom each set of balancing means comprising a main and an auxiliarycounterweight. The latter are guided in their movement by the respectiveguide members 48 and 49. If the sheaves and drums of a set be soconstructed, for example, as set forth in Fig. 8 of the drawings, as tohave identical angular rotation for all movement of the span, a singlerope v be may also be utilized for attachment to the span 55, as at 52.In this embodiment, a sheave 53 for the main counterweight 54, guided inguide member 54 and a drum'55 for the auxiliary counterweight 58, guidedin guide member 58,

may be made integral with each other or secured together, or their axlesmay be integrally united. This arrangement admits, also, of positioningthe auxiliary counterweight 60, Fig. 9, on the span side of its tower 6l, with the main counterweight 62 acting on the opposite side of thetower as in the previously described embodiment. The two saidcounterweights 6i) and 62 are guided respectively in the guide members63 and 64. I

' I claim:

1. In vertical liftapparatus: the combination acting in conjunction withthe main counterweight for substantially counterbalancing said span inall of its difierent vertical positions, and comprising an auxiliarycounterweight carried by the said supporting means, a drum mounted onthe sheave supporting means and provided with a spiral groove ofsubstantial lever arm throughout its operable portion, and a pluralityof flexible connections interconnecting the said counterweights, drumand vertical lift member and in all positions of the span substantiallyvertically disposed, one of which connections runs in the spiral grooveof said drum whereby vary-1 ing loads developed by the maincounterweight flexible connection in the diiferent positions of thevertical lift member are counterbalanced by the changing effectivemoment of the one drum connection as said connection wraps around saiddrum in the spiral groove thereof.

2. In vertical lift apparatus: the combination with a pair of verticalsupporting means, a vertical lift member movable'relatively theretobetween the same, a main counterweight for the lift member, and a sheavecarried'by one of the vertical supporting means for supporting said maincounterweight; of supplementary means acting in conjunction with themain counterweight for substantially counterbalancing said span in allof its different vertical positions,and

comprising an auxiliary counterweight carried and. ropes connecting themain counterweight with said drum, the respective connections in allpositions of the vertical lift member being substantially verticallydisposed and such as to effect opposing turning moments on the drum andone of the connecting ropes being wrappediaround the spiral. of .saiddrum. L

3. In vertical lift apparatus: the combination with a pair of verticalsupporting means, a vertical lift member movable relatively theretobetween the same, a main counterweight for. the lift member, and asheave carried by one of the vertical supporting means for supporting.said main counterweight; of supplementary means acting. in conjunctionwith the main counterweight for substantially counterbalancing said spanin all of its different vertical positions, and comprising an auxiliarycounterweight carried by the said supporting means, a drum mounted onthe sheave supporting means and provided with a spiral groove ofsubstantial lever arm throughout its operable portion, a rope connectingsaid auxiliary counterweight with the drum, and ropes connecting themain counterweight'with said drum,the respective connections in allposi-- tions of the vertical lift member being substantially verticallydisposed and such as .to effect opposing turning moments on the drum,and

the rope from the auxiliary counterweight being wrapped around thespiral of said drum.

4. In vertical lift apparatus: the combination with a pair of verticalsupporting means,'a vertween the same, a main counterweight for the liftmember, and a sheave carried by one of the vertical supporting means forsupporting said main counterweight; of supplementary means acting inconjunction with the main counterweight for substantiallycounterbalancing said span in all of its different vertical positions,and

comprising an auxiliary counterweight carried by the said supportingmeans, a drum mounted on the sheave supporting means, coaxial with saidsheave and connected therewith for like angular movement, said drumbeing provided with a spiral groove of substantial lever arm throughoutits operable portion, and a plurality of flexible connectionsinterconnecting the said counterweights, drum and vertical lift memberand in all positions of the span substantially vertically disposed, oneof which connections runs in the spiral groove of said drum wherebyvarying loads developed by the main counterweight flexible connection inthe different positions of the vertical lift member are counterbalancedby the changing effective moment of the one drum connection as saidconnection wraps around said drum in the spiral groove thereof.

5. In vertical lift apparatus: the combination with a pair of verticalsupporting means, a vertical lift member movable relatively theretobetween the same, a main counterweight for the lift member, and a'sheavecarried by one of the vertical supporting means for supporting said maincounterweight; of supplementary means acting in conjunction with themain counterweight for substantially counterbalancing said span in allof its different vertical positions, and comprising an auxiliarycounterweight carried by the said supporting means, a drum mounted onthe sheave supporting means, coaxial with said sheave and connectedtherewith for like angular movement, said drum being provided with aspiral groove of substantial lever arm throughout its operable portion,a rope connecting the sheave tical lift member movable relativelythereto bethe sheave and the drum and in all positions of the risingpart substantially vertically disposed, an axle supporting said drum, aspiral groove provided in said drum, said groove having a substantialvarying lever arm about said axle throughout its operable portion, oneof said flexible connections running in said groove, and saidcounterweights being so proportioned in relation to the lever arms ofsaid groove as to maintain a substantially exact balance of said risingpart, 3;

said counterweights and said flexible connections in all theirpositions.

THOMAS E. BROWN, JR.

